1. Field of the Invention
This invention deals with the hydrodewaxing of petroleum distillates thereby producing a treated product having an improved pour point. This invention deals with hydrodewaxing utilizing a ZSM-5 type catalyst. More particularly, this invention relates to novel dewaxing processes carried out in the presence of crystalline zeolitic material and, more particularly, to the removal of straight-chain paraffins and slightly branched-chain paraffins from hydrocarbon feedstocks by selectively converting these materials from a mixture of the same with the other components generally found in hydrocarbon feedstocks.
2. Description of Prior Art
Hydrocarbon conversion processes utilizing crystalline zeolites and, in particular, aluminosilicate catalysts have been the subject of extensive investigation during recent years as is obvious from both the patent and scientific literature. Crystalline aluminosilicates have been found to be particularly effective for a wide variety of hydrocarbon conversion processes and have been described and claimed in many patents including U.S. Pat. Nos. 3,140,249; 3,140,252; 3,140,251; 3,140,253; and 3,271,418. Aside from serving as general catalysts in hydrocarbon conversion processes, it is also known that the molecular sieve properties of zeolites can be utilized to preferentially convert one molecular species from a mixture of the same with other species.
In a process of this type a zeolite molecular sieve is employed having catalytic activity within its internal pore structure and pore openings such that one component of a feed is capable of entering within the internal pore structure thereof and being converted to the substantial exclusion of another component which, because of its size, is incapable of entering within the pores of the zeolitic material. Shape selective catalytic conversion is also known in the art and is disclosed and claimed in U.S. Pat. Nos. 3,140,322; 3,379,640 and 3,395,094.
Although a wide variety of zeolitic materials and particularly crystalline aluminosilicates have been successfully employed in various catalytic conversion processes, nevertheless, these prior art processes, in general, fell into one or two main categories. In one type of conversion process a zeolite was employed which had a pore size sufficiently large to admit the vast majority of components normally found in a charge, i.e., these materials are referred to as large pore size molecular sieves and they are generally stated to have a pore size of from 6 to 13 angstroms and are represented by zeolites X, Y and L. The other type of aluminosilicate was one which had a pore size of approximately 5 angstrom units and it was utilized to preferentially act upon normal paraffins to the substantial exclusion of other molecular species. Thus, by way of considerable over-simplification until recently, there were only two types of aluminosilicates which were available for hydrocarbon processing--those which would admit only normal paraffins and those which would admit all components normally present in a hydrocarbon feed charge. See U.S. Pat. No. 3,700,585 and Canadian Pat. No. 829,282.
It is well known in the art to form various lubricating oils, commonly referred to as lubes, from hydrocarbon fractions derived from petroleum crudes. With particular reference to the relatively waxy lube oils, a common procedure known in the art is to extract these hydrocarbon fractions with various solvents so as to give a raffinate of a desired high viscosity index, such material being resistant to changes in viscosity with changes in temperature and thus being useful under varying operating conditions. Moreover, it is particularly desired that the lube oil have a low pour point (A.S.T.M. Standard D97) so that it can be effectively used at low temperature conditions, since excessive thickening at low temperatures is often unacceptable. A related requirement for an acceptable lube oil is that it has a low cloud point, determined in accordance with the A.S.T.M. Cloud Point Test (A.S.T.M. D-2500), which fixes the temperature at which wax first starts to precipitate within the oil. Similarly, the freeze point (A.S.T.M. standard D-2836) and the Cold Filter Plugging Point (DIN 51428, SIS 155122, and AFNOR 549 Standards) are also further indicia of the fluidity of liquid hydrocarbons. Throughout the course of this specification it will be understood that when the term "pour point" is used, the comparable cloud point, freeze point or cold filter plugging point value might also be used as an equivalent term.